Drag factor - damper

Maintenance, accessories, operation. Anything to do with making your erg work.
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NickKira
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Drag factor - damper

Post by NickKira » January 9th, 2018, 11:11 am

I get that different damper settings on different machines can give the same drag factor, and that dust etc has an impact. The erg in the gym I go to gets a drag factor of 120 at damper 7, which seems a low DF based on what I've read (I'm no expert). Is this low? What does it mean (the erg has a lot or dust/lint? Little dust lint, i.e very clean so little drag?) Does it need a clean?

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hjs
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Re: Drag factor - damper

Post by hjs » January 9th, 2018, 11:35 am

NickKira wrote:I get that different damper settings on different machines can give the same drag factor, and that dust etc has an impact. The erg in the gym I go to gets a drag factor of 120 at damper 7, which seems a low DF based on what I've read (I'm no expert). Is this low? What does it mean (the erg has a lot or dust/lint? Little dust lint, i.e very clean so little drag?) Does it need a clean?
Its not very low, but the fan cage does how some does in it, still fine train, but cleaning would be nice.
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jackarabit
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Re: Drag factor - damper

Post by jackarabit » January 9th, 2018, 2:48 pm

Very clean means very much drag!

The C2 erg is an air pump. Air enters thru the adjustable valve or intake at the side typically called the damper or shutter because it regulates the dynamic pressure (cf/m) of air entering the fan shell. Ideally air exits thru the perforated steel band on the circumference of the fan shell which is in principle a very coarse screen or filter. As is the case with your typical forced air furnace filter, the openings in this shiny steel band are gradually occluded or restricted by the airborne particulates which it captures. Resulting back pressure in the fanshell compartment additionally restricts the volume of air entering thru the damper and the damper is opened to compensate the reduction of air available to be expelled by the fan.

Often too much emphasis is placed on cleaning the fan. Dust, pet/human dander, hair, and textile fiber clog the small ports in the perfmetal band long before they have a significant impact on the potential efficient operation of the fanblades. This is especially obvious in the public gym environment where textile fiber from gym clothes is a major source of airborne contamination not created by the one or two rowers who typically use an erg at home. Removing and cleaning the interior of the perfmetal band is a chore which may need doing once a yr. to a home erg whereas maintaining sufficient drag (training level rather than manufacturer specified) on a gym erg may mean cleaning six times or more per annum. I have personal experience with 1yr. old model Ds producing df85 @ damper setting 10--both YMCA gym machines. My home model D has never dropped below df170 @ damper 10 between semi-annual cleanngs.
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NickKira
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Re: Drag factor - damper

Post by NickKira » January 9th, 2018, 8:41 pm

Jack - thanks; great answer, i think that pretty much closes off that question
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Nick

Galley23
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Re: Drag factor - damper

Post by Galley23 » January 23rd, 2018, 4:01 am

I recently completed a 10sec watt test on my C2 at home, DF 200 as per test protocol. I made 3 attempts and could not beat 650watts. I didn't feel too bad until my team mates who did the rest at club were coming back with figures in 700,800 and some 900s. My 2k would be one of the strongest so I put it down to fitness and efficiency. That was until I was at the club last week and without a warmup, cranked DF up to 200. Performing the test once I was surprised to see that I was easily over 700 ad reached 750. My machine is 7 years old and clubs are newer. I would have also preferred doing my 2ks on clubs machines as it did always feel easier but this is proof that DF is not consistent across machines. I have searched for similar stories in google but cannot find anything that goes against DF being a universal benchmark. Can anyone explain this and if there is a fix. I did my PB on my home machine years ago so it must have been ok at some point.

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hjs
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Re: Drag factor - damper

Post by hjs » January 23rd, 2018, 10:39 am

Galley23 wrote:I recently completed a 10sec watt test on my C2 at home, DF 200 as per test protocol. I made 3 attempts and could not beat 650watts. I didn't feel too bad until my team mates who did the rest at club were coming back with figures in 700,800 and some 900s. My 2k would be one of the strongest so I put it down to fitness and efficiency. That was until I was at the club last week and without a warmup, cranked DF up to 200. Performing the test once I was surprised to see that I was easily over 700 ad reached 750. My machine is 7 years old and clubs are newer. I would have also preferred doing my 2ks on clubs machines as it did always feel easier but this is proof that DF is not consistent across machines. I have searched for similar stories in google but cannot find anything that goes against DF being a universal benchmark. Can anyone explain this and if there is a fix. I did my PB on my home machine years ago so it must have been ok at some point.
Did you really check your drag back home? Thats not setting it on 10, but really check the drag. 200 is also not max, 220/230 is. On a really ciean one at sealevel. Air temp also matters. Colder air is havier, giving more drag.
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Re: Drag factor - damper

Post by Galley23 » January 23rd, 2018, 12:22 pm

I did check drag factor, 10sec protocol says to use DF of 200 so I set home machine to 200, made 3 attempts just touching 650. Setting the club machine to 200 I was able to reach 750 without too much thought. If i had time for another 1 or 2 goes I would have passed 750. I know air temp affects drag but isnt that what setting the DF is supposed to equalise? I might not have been clear on last blog but I have preferred to do my 2K on the club machine over the past few years as it felt faster. I had no real concrete evidence to say this was nothing more than psychological. However if the max wattage on my home machine is 100 less than the club machine with same DF then it gives evidence to the point. Has anyone else got the same experience? Why does this happen, is there a fix? It kinda messes up training splits etc.

John

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hjs
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Re: Drag factor - damper

Post by hjs » January 23rd, 2018, 12:46 pm

Galley23 wrote:I did check drag factor, 10sec protocol says to use DF of 200 so I set home machine to 200, made 3 attempts just touching 650. Setting the club machine to 200 I was able to reach 750 without too much thought. If i had time for another 1 or 2 goes I would have passed 750. I know air temp affects drag but isnt that what setting the DF is supposed to equalise? I might not have been clear on last blog but I have preferred to do my 2K on the club machine over the past few years as it felt faster. I had no real concrete evidence to say this was nothing more than psychological. However if the max wattage on my home machine is 100 less than the club machine with same DF then it gives evidence to the point. Has anyone else got the same experience? Why does this happen, is there a fix? It kinda messes up training splits etc.

John
Clear john.

If you pull so much less, every session home should be a lot slower.

I have used lots of machines and only when there is really trouble, think rusty chain, seat not smooth it slows you down.
If you have a ok ish erg and use the same drag outcome will not vary. Your 100 watts extra on 650 is wierd.
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Re: Drag factor - damper

Post by Galley23 » February 6th, 2018, 3:24 am

Anyone else want to jump in here. I have now set up both machines next to each other. I have tested each machine 2-4 times at different drag factors. E.g both at df 200 , 100mins intervals 6 min rest and done 3 intervals at each DF. The results are always the same with up to 7 secs difference in split times. I cannot get under 1:21 on slower machine but can get to 1:15 in other. SPM etc were all pretty controlled. I have been rowing for 30 years so please don't ask me to try this or that. I want to know if anyone else sees this and how to fix it.

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Re: Drag factor - damper

Post by jamesg » February 6th, 2018, 4:26 am

Maybe by exclusion. Try swapping the PMs, if identical. No doubt you've already checked the PM - machine type coordination and settings.

There must be something substantial, 1:15 / 1:21 time ratio is 92.6%, so about 80% Power ratio: too big for anything mechanical. Possibly a magnet missing or not acting in one of the flywheels, but 80% doesn't look right for that.

Do you see similar force curves?
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Galley23
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Re: Drag factor - damper

Post by Galley23 » February 6th, 2018, 12:27 pm

jamesg wrote:Maybe by exclusion. Try swapping the PMs, if identical. No doubt you've already checked the PM - machine type coordination and settings.

There must be something substantial, 1:15 / 1:21 time ratio is 92.6%, so about 80% Power ratio: too big for anything mechanical. Possibly a magnet missing or not acting in one of the flywheels, but 80% doesn't look right for that.

Do you see similar force curves?
Thanks - thats some good advice. I will try the swapping the PM's to isolate the issue. I haven't checked the force curves but I assume I would be looking for a change in pattern or if pattern is the same it is the PM?

When you say, "check the PM, Machine type , settings etc." can you extrapolate. I have read some comments in relation to having PM set up for the right machine. I can check this but I do not have a memory of ever changing the PM etc. in fact I have had the machine for nearly 10 years, used it each week and never had to change the battery (not that I can remember anyway). Is there a chance the PM has defaulted to the wrong model?

Have felt the difference for about 3 years (at home vs club house) but always put it down to being in my head or environment (I have always set best times in the colder months). We recently did some 10 sec power tests which showed up these differences, even side by side in same conditions.

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Re: Drag factor - damper

Post by Neil Hitt » February 20th, 2018, 8:54 am

i have been thinking about this as I too have an ageing model c . I have refitted with a PM5 and love it , however I have noticed the DF changing during a workout slightly.. maybe from 134 down to 131 over an hour. Almost like something is warming up and becoming easier to spin or visa versa..

I was wondering if the freewheel in the drive cog could be an issue. I have not dived in with the spanners but i am assuming this might be full if grease or in some way providing additional drag to the flywheel thus upsetting the slowing down of the flywheel and screwing up the calibration ?? It wouldn't just be the drag caused by the air through the machine in that case as during the drive phase the freewheel would be locked so the Work would be coming form the air alone. then on recovery if there was some additional slowing forces being added by the chain and flywheel it might cause the flywheel speed decay to miscalculate the PM5 ??

Have i been kidding myself with some good times !!! or bad times ??

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